1. Field of the Invention
This invention relates generally to fasteners, and more particularly relates to pull stem fasteners which can have either a collar swaged onto them or a female threaded device, such as a threaded nut or a threaded collar, torqued onto them.
2. Description of the Related Art
Fasteners of the type used in the aerospace industry, include those that are installed by a swaging operation and those that have a female threaded device, such as a threaded nut or a threaded collar, torqued onto them. Swaging is a process for reducing the cross-sectional area of a part by using a hammer-type or ram-type of tool to apply compressive forces to the outside surface of the part. Swaging operations for a fastener include sliding a swage collar over a portion of a fastener having a series of lock grooves. The swage collar includes an inside surface which is typically smooth and sufficiently large to fit over the lock grooves of the fastener with a clearance fit. The swage collar also includes sufficient thickness so that when the swaging operation is performed, material from the swage collar can be forced into the lock grooves on the fastener, thereby locking the swage collar to the fastener. Since the swage collar material must be forced into the lock grooves, the swage collar material is typically softer than the material incorporated in the lock grooves.
Fasteners which are installed by a swaging operation generally include those having a pull stem portion and those which do not have a pull stem portion. Fasteners having the pull stem portion include a pin having an enlarged protruding head at a proximal end of the fastener. The head includes a distal surface which contacts a surface of a workpiece. Distal the head is a smooth shank portion which is adapted to be received within substantially aligned holes within a series of workpieces. The smooth shank portion may provide either a clearance fit or an interference fit with the aligned holes in the workpiece. Distal the smooth shank portion is a lock shank portion having a plurality of circumferentially extending annular lock grooves. Alternatively, some pins include lock grooves having a helical pattern rather than the annular pattern. The lock grooves are configured to engage a swage collar through a swage operation. Distal the lock shank portion is a pull stem portion which may be separated from the lock shank portion by a breakneck groove.
To install the pin, the pull stem portion is inserted into the aligned holes within the series of workpieces until it protrudes from the hole on the opposite side of the workpiece. For pins having an interference fit at the smooth shank portion, a tool is used to pull the smooth shank portion into the hole by pulling on the pull stem portion until a distal surface on the head contacts a surface of the workpiece. Having an interference fit, the pin is retained within the workpiece by compressive forces from at least one of the aligned holes applied to the smooth shank portion. At this point, the tool may continue to pull on the pull stem portion until a sufficient tensile force is attained to sever the pull stem portion from the remainder of the pin at the breakneck groove. Then the swage collar may be slid over the lock shank portion and swaged into place.
To install a pin having a smooth shank portion which provides a clearance fit, the pull stem portion is inserted into the aligned holes and advanced through the hole until the distal surface of the head contacts a surface of the workpiece. The swage collar may then be slid over the lock shank portion preparatory to the swaging operation. The tool may apply a light tensile load on the pull stem portion during the swaging operation to hold the pin in place. Alternatively, to have the pin remain in tension after the swaging operation, the tool may apply a relatively high tensile load on the pull stem portion during the swaging operation, thereby locking the fastener in a preloaded condition. After the swage collar is swaged onto the lock grooves, the pull stem portion may be pulled in tension further until it severs from the remainder of the pin at the breakneck groove.
Fasteners which are installed by a swaging operation that do not include a pull stem portion include a pin having an enlarged protruding head, a smooth shank portion and a lock shank portion. As with the fasteners which include a pull stem portion, the smooth shank portion is adapted to be received within aligned holes within a series of workpieces and may provide either a clearance fit or an interference fit. Also similar to the fasteners which include the pull stem portion, the lock shank portion may include either a plurality of circumferentially extending annular lock grooves or lock grooves having a helical pattern.
To install a fastener which includes a smooth shank portion having an interference fit and no pull stem portion, the lock shank portion is inserted into the aligned holes within the series of workpieces from one side until it protrudes from the opposite side of the workpieces. A tool may be used to pull the smooth shank portion into the aligned holes by pulling on the lock shank portion until the distal surface of the head contacts the workpiece. The pin is retained within the workpiece by compressive forces of at least one of the aligned holes applied to the smooth shank portion. With the pin thus retained, the swage collar may be slipped over the lock grooves and a tool may then swage the collar onto the lock grooves of the lock shank portion.
Fasteners which include a smooth shank portion having a clearance fit and no pull stem portion may include a threaded hole on a surface at the distal end of the fastener, or some other means through which the tool may engage the lock shank portion of the pin in order to retain the pin for the swage operation. To install such a fastener, the lock shank portion is inserted into the aligned holes within the series of workpieces from one side until it protrudes from the opposite side of the workpieces and the distal surface of the head contacts the workpiece. The swage collar may then be slid over the lock shank portion preparatory to the swaging operation. The tool may apply a light tensile load to the pin through the threaded hole or other tool engagement means during the swaging operation to hold the pin in place. Alternatively, to have the pin remain in tension after the swaging operation, the tool may apply a relatively high tensile load through the threaded bole or other engagement means during the swaging operation, thereby locking the fastener in a preloaded condition.
Fasteners which are installed by having a threaded nut or a threaded collar torqued onto them also include those having a pull stem portion and those which do not have a pull stem portion. Fasteners having the pull stem portion include a pin having an enlarged protruding head at a proximal end of the fastener and having a distal surface which contacts a surface of a workpiece. Adjacent the head is a smooth shank portion which is adapted to be received within the aligned holes within the series of workpieces. The smooth shank portion may provide either a clearance fit or an interference fit with the aligned holes in the workpiece. Distal the smooth shank portion is a threaded shank portion which may include a standard thread for receiving a threaded nut or a threaded collar. Distal the threaded shank portion is a pull stem portion which may be separated from the threaded shank portion by a breakneck groove.
Installing the pin which is configured to have a threaded nut or a threaded collar torqued onto it and having a pull stem portion is similar to installing the pin which is configured to be installed through a swaging operation which includes a pull stem portion. The pull stem portion is inserted into the aligned holes within the workpiece until it protrudes from the opposite side of the workpiece. For pins having an interference fit at the smooth shank portion, a tool is used to pull the smooth shank portion into the aligned holes by pulling on the pull stem portion until the distal surface on the head contacts a surface of the workpiece. Having an interference fit, the pin is retained within the workpiece by compressive forces from at least one of the aligned holes applied to the smooth shank portion. The tool may continue to pull on the pull stem portion until a sufficient tensile force is attained to sever the pull stem portion from the remainder of the pin at the breakneck groove. Then, the threaded nut or the threaded collar may be torqued onto the threaded shank portion of the pin.
To install the threaded pin having a smooth shank portion which provides a clearance fit, the pull stem portion is inserted into the aligned holes and advanced through the aligned holes until the distal surface of the head contacts a surface of the workpiece. The threaded nut or threaded collar may then be slid over the pull stem portion. Then, while applying a light tensile load onto the pull stem portion, the threaded nut or threaded collar may be torqued onto the threaded shank portion. Alternatively, to place the fastener in a preload condition, the tool may apply a relatively high tensile load on the pull stem portion during the torquing operation. After the threaded nut or threaded collar is torqued onto the threaded shank portion, the pull stem portion may be pulled in tension further until it severs from the remainder of the pin at the breakneck groove.
Fasteners which are installed by having a threaded nut or a threaded collar torqued onto them that do not include a pull stem portion include a pin having an enlarged protruding head, a smooth shank portion and a threaded shank portion. As with the fasteners which include a pull stem portion, the smooth shank portion is adapted to be received within aligned holes within a series of workpieces and may provide either a clearance fit or an interference fit.
To install the threaded pin which includes a smooth shank portion having an interference fit and no pull stem portion, the threaded shank portion is inserted into the aligned holes within the series of workpieces from one side until it protrudes from the opposite side of the workpiece. A tool may be used to pull the smooth shank portion into the aligned holes by pulling on the threaded shank portion until the distal surface of the head contacts the workpiece. The pin is retained within the workpiece by compressive forces of at least one of the aligned holes applied to the smooth shank portion. With the pin thus retained, the threaded nut or threaded collar may be torqued onto the threads of the threaded shank portion.
Threaded pins which include a smooth shank portion having a clearance fit and no pull stem portion may include a threaded hole on a surface at the distal end of the fastener, or some other means through which the tool may engage the threaded shank portion of the pin in order to retain the pin for the torquing operation. To install these fasteners, the threaded shank portion is inserted into the aligned holes within the series of workpieces from one side until it protrudes from the opposite side of the workpiece and the distal surface of the head contacts the workpiece. The threaded nut or threaded collar may then be torqued onto the threaded shank portion. To torque the threaded nut or threaded collar onto the pin, the tool may apply a light tensile load to the pin through the threaded hole or other tool engagement means to hold the pin in place. Alternatively, to place the pin in a preloaded condition, the tool may apply a relatively high tensile load through the threaded hole or other engagement means during the torquing operation.
As both fasteners which are installed by a swaging operation and fasteners which are installed by having a threaded nut or a threaded collar torqued onto them are popular in industry, such as the aircraft industry, manufacturers inventory both types of fasteners. Inventorying and using multiple types of fasteners adds significant costs to the production of aircraft. Hence, those skilled in the art have recognized a need for a fastener which can be used with multiple installation means so that the quantity of fastener types used by aircraft manufactures can be reduced.
Briefly, and in general terms, the present invention is directed to a fastener which can be installed into a workpiece by either swaging or torquing methods so that the types of fasteners used by manufacturers can be reduced.
In one currently preferred aspect of the invention, the fastener includes an enlarged protruding head which is substantially centered about a longitudinal axis and positioned at a proximal end of the fastener. The fastener also includes a substantially cylindrical smooth shank portion which is positioned distal and adjacent the head and substantially centered about the longitudinal axis. The smooth shank portion includes a first diameter. A threaded shank portion distal to the smooth shank portion and is substantially centered about the longitudinal axis. The threaded shank portion includes a male thread which is sufficiently strong to have a swage collar of a softer material swaged onto it without appreciable damage to the threads. The male thread has a second diameter smaller than the first diameter of the smooth shank portion. The fastener also includes a pin tail portion. The pin tail portion is positioned distal to the threaded shank portion and is substantially centered about the longitudinal axis. The pin tail portion includes means for a tool to engage the pin tail portion and pull the fastener in tension. The pin tail portion also includes a third diameter which is smaller than the second diameter of the threaded shank portion. Further, a swage collar or a female threaded device which is intended to be engaged with the threaded shank portion of the fastener fits over the pin tail portion without any interference. The fastener also includes a breakneck groove which includes a fourth diameter which is smaller than the third diameter of the pin tail portion and is positioned between the threaded shank portion and the pin tail portion and substantially centered about the longitudinal axis. The breakneck groove is controlled to ensure that the breakneck groove includes a lower tensile strength than any other portion of the fastener and that the fastener will sever at the breakneck groove when a preset range of tension is applied to the fastener at the pin tail portion.
In a detailed aspect of the currently preferred embodiment of the invention, the length of the smooth shank portion is sufficient to protrude from a surface on a second side of the at least one workpiece while a distal surface of the head is in contact with a surface on a first side of the at least one workpiece. In another currently preferred embodiment, the length of the smooth shank portion is insufficient to protrude from a surface on a second side of the at least one workpiece while the distal surface of the head is in contact with a surface on a first side of the at least one workpiece. The means for the tool to engage the pin tail portion may include a plurality of circumferentially extending annular grooves. In a further currently preferred embodiment, the tensile strength of the breakneck groove is controlled through the fourth diameter of the breakneck groove and the strength of the fastener material in the region of the breakneck groove. In an additional currently preferred embodiment, the breakneck groove includes a first conically tapered surface which tapers distally from the threaded shank portion toward the longitudinal axis of the fastener. The breakneck groove also includes a second conically tapered surface which tapers proximally from the pin tail portion toward the longitudinal axis of the fastener. A substantially circumferential intersection is positioned between the first and second conically tapered surfaces. Further, a radius having a controlled dimension is positioned at the intersection of the first conically tapered surface and the second conically tapered surface.
In a second currently preferred aspect of the invention, the fastener may be installed through a swaging operation. The method for installing the fastener by swaging includes providing the fastener and at least one workpiece. The at least one workpiece includes a hole therethrough which provides a clearance fit with the smooth shank portion of the fastener. The pin tail portion of the fastener is inserted into the hole within the at least one workpiece from a first side of the at least one workpiece. The fastener is advanced distally until the pin tail portion protrudes from a surface on a second side of the at least one workpiece and the distal surface of the head of the fastener contacts a surface on the first side of the at least one workpiece. A further step includes providing a swage collar which includes a substantially smooth interior surface and provides a clearance fit between the swage collar and the threaded shank portion. The swage collar is slid proximally over the pin tail portion and threaded shank portion of the fastener until the swage collar is positioned proximate the second side of the at least one workpiece. A tool engages the pin tail portion and pulls the fastener distally in tension. The tool also pushes the swage collar proximally against the second side of the at least one workpiece and swages the swage collar onto the threaded shank portion of the fastener until the swage collar substantially fills the threads on the threaded shank portion. With the swage collar swaged onto the threaded shank portion of the fastener, the tool increases tension at the pin tail portion of the fastener until the preset range of tension has been attained and the fastener severs at the breakneck groove.
In a third currently preferred aspect of the invention, the fastener may be installed through a torquing operation. This method includes providing the fastener and at least one workpiece. The at least one workpiece includes a hole therethrough which provides a clearance fit with the smooth shank portion of the fastener. The pin tail portion of the fastener is inserted into the hole within the at least one workpiece from a first side of the at least one workpiece. The fastener is advanced distally until the pin tail portion protrudes from a surface on a second side of the at least one workpiece and the distal surface of the head of the fastener contacts a surface on the first side of the at least one workpiece. A further step includes providing the female threaded device and sliding the female threaded device proximally over the pin tail portion. A tool engages the pin tail portion and pulls the fastener distally in tension while preventing the fastener from turning. The tool also torques the female threaded device onto the threaded shank portion until a desired torsional load is attained. With the female threaded device torqued onto the fastener, the tool increases the tension at the pin tail portion of the fastener until the preset range of tension has been attained and the fastener severs at the breakneck groove.
In a fourth currently preferred aspect of the invention, the fastener may be installed through a torquing operation. This method includes providing the fastener and at least one workpiece. The at least one workpiece includes a hole therethrough which provides an interference fit with the smooth shank portion of the fastener. The pin tail portion of the fastener is inserted into the hole within the at least one workpiece from a first side of the at least one workpiece and advanced distally until the pin tail portion protrudes from a surface on a second side of the at least one workpiece. A tool engages the pin tail portion and pulls the smooth shank portion of the fastener distally into the hole within the at least one workpiece until the distal surface of the head of the fastener contacts a surface on the first side of the at least one workpiece. The tool increases tension at the pin tail portion of the fastener until the preset range of tension has been attained and the fastener severs at the breakneck groove. A further step includes providing the female threaded device. The female threaded device is torqued onto the threaded shank portion through the use of the tool until a desired torsional load is attained.
From the above, it may be seen that the invention provides for a configuration of a fastener which can be installed through either a swaging operation or a torquing operation. Further, the invention includes installation methods using swaging operations and torquing operations. These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.